Background Squat exercises have been widely employed in fitness, rehabilitation, sports performance, and strength training under either free weight or weight-bearing conditions. Objectives To report the evidence regarding the core contribution of biomechanical changes in the trunk and lower limbs of physical practitioners. Performance outcomes from engaging core activity during squat exercises with various recruitment techniques were analyzed, specifically including the abdominal brace (AB), abdominal hollow (AH), abdominal drawing-in maneuver (DIM), and volitional preemptive abdominal contraction (VPAC). Method Four electronic databases, PUBMED, WEB of SCIENCE, Google Scholar, and SCOPUS, were searched until 1st April 2024. Study methodological quality was scored by two independent researchers using the modified Downs and Black checklist. Biomechanical studies focusing on the effects of core recruitment techniques on the lower extremities in deep squats were systematically reviewed. Dependent variables were analyzed as indicators of full squats for training, rehabilitation, and fitness exercise. Results Six articles fulfilled the eligibility criteria. The evidence indicated that core recruitment techniques during deep squats could increase lower limb muscle activation, specifically the rectus femoris, biceps femoris, and gluteus maximus, and body stability at depth squats and avoid potential injury. Further evidence indicated that core recruitment techniques could have a positive effect on lower limb kinematics during squatting, providing evidence for squatting as a rehabilitation exercise. Conclusions The findings indicate that core engagement may affect the trunk, lower limbs, and athletic performance. Differences in the effects among the existing studies were possibly due to the limited scope of these studies. Further exploration is needed for a comprehensive and consistent understanding of this complex issue.
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